There are more workflow activities that you can use beside the one that are already in, for example "Create Task".
To add them to the toolbox you need to open visual studio and on the Toolbox section:
1. Create new tab by right click and select "Add Tab".
2. Under the new tab press right click and select "Choose Items…" (It will take a while to open).
3. Then select microsoft.sharepoint.WorkflowActions.dll, it is usually under C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\ISAPI